Formal canonization is a lengthy process often taking many years, even centuries. The first step in this process is an investigation of the candidate's life, undertaken by an expert. After this, the report on the candidate is given to the bishop of the area and more studying is done. It is then sent to the Congregation for the Causes of Saints in Rome. If they approve it, then the person may be granted the title of "Venerable", further investigations may lead to the candidate's beatification and given title of "Blessed." At a minimum, two important miracles are required to be formally declared a saint (this requirement can be waved in the case of martyrs). The Church, however, places special weight on those miracles or instances of intercession that happened after the individual died and which are seen to demonstrate the saint's continued special relationship with God after death. Finally, when all of this is done the pope canonises the saint. -- Saint - Wikipedia, the free encyclopedia

In the Roman Catholic Church and the Eastern Catholic Churches in communion with Rome, the act of canonization is reserved to the Holy See and occurs at the conclusion of a long process requiring extensive proof that the person proposed for canonization lived and died in such an exemplary and holy way that he or she is worthy to be recognized as a saint. The church's official recognition of sanctity implies that the persons are now in heavenly glory, that they may be publicly invoked and mentioned officially in the liturgy of the church, most especially in the Litany of the Saints in the Canon of the Mass. -- Canonization - Wikipedia Article